Electric power blade-type disconnect switches utilize elongated blade arms to make physical and electrical connections at high voltages, such as sub-transmission and transmission voltages. The blade arms pivot into and out of connection with a receptacle typically referred to as the jaws. When the blade is in the closed position but not properly engaged within the jaws, the loose connection generates arcing that can damage the blade and jaws and inject unwanted noise onto the electrical system. A variety of techniques have therefore been developed to ensure that the blade arm makes a good physical and electrical connection with the jaws when the switch is closed. In particular, the blade arm typically rotates as it comes into contact with the jaws to form a tight interference fit with leaf springs within the jaws often referred to as the fingers. This causes the blade to first enter into the jaws, and then rotate so that it is squeezed between the leaf springs of the jaws, to create an interference fit ensuring a solid mechanical fit and a good (non-arcing) electrical connection between the blade and the jaws.
The blade and jaws are ordinarily exposed to the elements during normal operations. The conventional rotating blade connection works well provided that the there is no physical interference between the blade and jaws. During winter storms, however, ice can accumulate on the blade and jaws causing the blade to remain outside the jaws after the closing action. When the blade is in close proximity but not fully received and rotated into proper engagement within the jaws, the blade is close enough for arcing to develop between the blade and jaws. In addition, it may be difficult for a technician to visibly detect the poor connection when inspecting the switch from the ground, particularly during poor weather. Moreover, power line faults often occur during poor weather, making switch operation more likely. The resulting poor connection may not be detected until significant damage has been incurred by the switch. An arcing contact may also inject current spikes into the power line, which can be potentially damaging to sensitive devices, such as computers and other electronic devices.
Techniques used in prior detectors to indicate a properly engaged closed position requires a technician to look at the rotation of a “vertical pipe” that is part of the switch linkage, but visually inspecting the linkage is difficult from the ground, which is a long distance for viewing. The difficulty is complicated by the fact that there are a number of different types of mechanical malfunctions that can occur between the linkage and the critical elements of the blade and jaws. Significant operational difficulties can occur if there are false indications of proper engagement. Relying on the position of the “vertical pipe” in the linkage as the only indication of proper engagement of the blade within the jaws has resulted in too many failures of technicians to detect improper engagement of the blade within the jaws. Even experienced technicians can fail to determine the actual state of blade engagement and the error rate increases when with lower level of experience of the technicians.
As a result, there is significant need for a more reliable and prominently visible blade closing detector to prevent false indications of proper blade engagement and the resulting damage that can occur from improper blade engagement.